Type Of Martensitic Transformation Research Articles

Transformation of cuprite to tenorite through a martensitic-like type process in copper-doped glasses annealed in reduced atmosphere with the metal copper formation

The incorporation of copper nanoparticles into the glass matrix has attracted great interest in many fields due to their significant physical and chemical properties and their applications (e.g. opto-electronic and bio-medical tools). Several methodologies, such as the doping method and subsequent annealing of the glass in oxidizing and reducing atmospheres to synthesize copper nanoparticles in a glass are widely used. In this work, the doping method and subsequent annealing of the glass in a Ar/H2 atmosphere has been used. This treatment caused a martensitic-type transformation which, to our knowledge, has not been mentioned in the literature. The result was the transformation from cuprite to tenorite about 300°C, and the presence of dispersed rounded and polyhedral copper nanoparticles and dendritic shapes of nanoparticles. The reaction of CuO and H2, between 250 and 300°C, originated metallic copper particles. The mechanism of the martensitic-type transformation has been derived from the characterization results of copper-doped glasses annealed in reduced atmosphere by optical microscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. The martensitic-like type structure could have imparted shape memory characteristics to the copper-doped glasses annealed in reduced atmosphere, opening a window for future research.

A new understanding of transformation induced plasticity (TRIP) effect in austenitic steels

Zackay et alproposed the transformation induced plasticity (TRIP) effect in the study of austenitic steels in 1967, and they emphasized that the TRIP effect is caused by an increase in strain hardening rate (SHR) due to strain-induced martensitic transformation (SIMT), but they do not specify what kind of SIMT is. To do this, we modeled their experiments of A-1 steel and A-2 steels in this work, and used the microstructural characterization of X-ray diffraction and transmission electron microscopy to obtain a new understanding of the TRIP effect in austenitic steels. There are two types of martensitic transformations: FCC γ → HCP ε-martensite and FCC γ →BCC α-martensite in pre-deformation A-2 steel, and in the early stage of deformation during tension, the considerable amount of strain-induced HCP ε-martensite leads to a low SHR, but in the late stage of deformation, the almost single strain-induced BCC α-martensite leads to a high SHR. Further experiment gives an amazing result: considerable Dislocations Across Martensite/Austenite Interface (DAMAI) move from martensite into austenite during deformation, which results in the rapid increase of dislocation density in austenite accompanying with the 233 MPa increment of flow stress, being higher than the 167 MPa increment from SIMT, therefore, in two main deformation mechanisms for the strength and plasticity enhancement of austenitic steels the contribution of DAMAI effect on SHR is greater than that of SIMT on SHR proposed by Zackay et al. Besides, since dislocations cannot move from HCP ε-martensite to FCC γ-austenite because the generation condition of DAMAI are not met, there are no DAMAI phenomenon, which results in a low SHR.

Theoretical study on martensitic-type transformation of rutile, columbite, and baddeleyite phase of TiO2

The martensitic-type phase transition pathways between any two among rutile, columbite-type, and baddeleyite-type phase of TiO2 are studied with linear interpolation and G-SSNEB methods within first-principles calculations. Our theoretical simulations reveal that the reverse transition from the rutile to the columbite-type phase should be realized easily at above 550 °C because its theoretical potential barrier of phase transition is basically the same as the average kinetic energy of molecule unit at 550 °C. The phase transitions of columbite-type to baddeleyite-type and rutile to baddeleyite-type are two-step transitions in which the crystal volume should be compressed to a certain extent at first, and then the atoms of alternative (200) and (002) crystal plane begin to shuffle, at the same time the crystal cell begins to shear. Their phase transition resistance originates from the crystal shear rather than atomic shuffles of alternative (200) and (002) crystal plane. Our theoretical calculations give the reason why the baddeleyite-type crystal phase cannot return to rutile phase but to columbite-type phase after depressurization.

Theoretical study on martensitic-type transformation path from rutile phase to α-PbO2 phase of Ti2O**Project supported by the National Natural Science Foundation of China (Grant Nos. 51872227, 51572219, and 11447030).

The martensitic-type phase transformation paths from the rutile to the α-PbO2 phase of TiO2 are studied with linear interpolation and NEB/G-SSNEB methods based on first-principles calculations. Its potential energy surface and the lowest energy path are revealed. Our results indicate that the titanium atoms of the rutile phase shuffle along the [0–11]rut crystal direction to form the α-PbO2 phase. During the phase transition, the oxygen atoms are dragged by the heavier titanium atoms and then reach their new equilibrium positions. The barrier of phase transition from nudged elastic band theory is about 231 meV, which is qualitatively consistent with previous theoretical calculations from the monoclinic phase to the tetragonal phase for ZrO2 and HfO2. Debye model can also be successfully used to predict the pressure and temperature of the phase transformation.

Elastocaloric Effect Associated with Different Types of Martensitic Transformations: Typical First‐Order and Weak First‐Order Ones

Elastocaloric effects of a Ni50Fe19Ga27Co4 alloy exhibiting a typical first‐order martensitic transformation (MT) and an Fe‐31.2Pd (at.%) alloy exhibiting a weak first‐order MT, respectively, have been compared using their single crystals. A flat region appears in the temperature dependence of elastocaloric effect in the Ni50Fe19Ga27Co4 alloy, while such region is missing in the Fe‐31.2Pd alloy. The elastocaloric effect of the Ni50Fe19Ga27Co4 alloy originates essentially from the latent heat released by the stress‐induced MT, while that in the Fe‐31.2Pd alloy originates essentially from the entropy change caused by elastic deformation of the parent and martensite phases. Although the Young's modulus in the [001] direction at Ms is nearly the same for the two alloys (E ∼ 2 GPa), its slope dE/dT is largely different between the two alloys. It is approximately 0.003 GPa K−1 for the Ni50Fe19Ga27Co4 alloy and 0.2 GPa K−1 for Fe‐31.2Pd alloy.

Lattice Softening in Fe3Pt Exhibiting Three Types of Martensitic Transformations

We have investigated the relation between the softening of elastic constants and martensitic transformation in Fe3Pt, which exhibits various kinds of martensitic transformation depending on its long-range order parameter S. The martensite phases of the examined alloys are BCT (S = 0.57), FCT1 (S = 0.75, c/a < 1) and FCT2 (S = 0.88, c/a > 1). The elastic constants C′ and C44 of these alloys decrease almost linearly with decreasing temperature. Although the temperature coefficient of C′ decreases as S increases, C′ at the transformation temperature is the smallest in the alloy with S = 0.75, which transforms to FCT1. This result implies that softening is most strongly related to the formation of the FCT1 martensite with tetragonality c/a < 1 among the three martensites.

Quantification of dislocations densities in zirconium hydride by X-ray line profile analysis

Zirconium-based components in nuclear power plants are embrittled by precipitates of δ zirconium hydride, which involves a martensitic-type transformation of the hexagonal α-Zr lattice into the face-centered cubic Zr sublattice of the hydride. As a result, the hydride precipitates have a complex and heavily distorted internal structure that manifests as broad peaks in X-ray diffraction experiments. By a detailed analysis of the peak widths measured for different crystal planes we have found that most of this broadening is the result of dislocations. The analysis also showed that δ-hydride has very anisotropic mechanical elastic properties, in agreement with ab-initio simulations presented in the literature.Provided with this peak-broadening model, we have quantified dislocation densities within δ-hydrides precipitated in several Zr alloys, by analyzing previously published X-ray diffraction experiments performed at three synchrotron X-ray sources. The specimens investigated correspond to components affected by different hydride embrittling processes, namely: (i) samples from various components, charged in the laboratory with H contents in the ∼250 wt ppm range, (ii) laboratory-produced hydride blisters in Zr2.5%Nb pressure tubes; and (iii) Zircaloy-4 specimens machined from cooling channels of Atucha I nuclear power plant after 10 years in-service, containing ∼140 wt ppm of equivalent H content and subjected to an estimated fast neutron fluence of ∼1022 neutrons/cm2. Results show that dislocations densities in the δ-hydrides are large (5–20 × 1015 cm−2) and vary among the different specimens. We also found that dislocations densities in the hydride are proportional to the fraction of hydrides already formed in the matrix, which was interpreted as the effect of matrix hardness in the precipitate structure.

Deformation mechanisms of a 20Mn TWIP steel investigated by in situ neutron diffraction and TEM

The deformation mechanisms and associated microstructure changes during tensile loading of an annealed twinning-induced plasticity steel with chemical composition Fe–20Mn–3Si–3Al–0.045C (wt.%) were systematically investigated using in situ time-of-flight neutron diffraction in combination with post mortem transmission electron microscopy (TEM). The initial microstructure of the investigated alloy consists of equiaxed γ grains with the initial α′-phase of ∼7% in volume. In addition to dislocation slip, twinning and two types of martensitic transformations from the austenite to α′- and ε-martensites were observed as the main deformation modes during the tensile deformation. In situ neutron diffraction provides a powerful tool for establishing the deformation mode map for elucidating the role of different deformation modes in different strain regions. The critical stress is 520MPa for the martensitic transformation from austenite to α′-martensite, whereas a higher stress (>600MPa) is required for actuating the deformation twin and/or the martensitic transformation from austenite to ε-martensite. Both ε- and α′-martensites act as hard phases, whereas mechanical twinning contributes to both the strength and the ductility of the studied steel. TEM observations confirmed that the twinning process was facilitated by the parent grains oriented with 〈111〉 or 〈110〉 parallel to the loading direction. The nucleation and growth of twins are attributed to the pole and self-generation formation mechanisms, as well as the stair-rod cross-slip mechanism.

Memory Effect in Thin Thermocycling-modified La0.67Ca0.33MnO3 Films

Nonhomogeneous thin La 0.67 Ca 0.33 MnO 3 films, having T m in 180 K – 200 K temperature range, were thermocycled between 80 K and 210 K using liquid nitrogen. After the thermocycling it was confirmed formation of highly resistive state with additional low temperature peak of resistance with maximum at 115 K when measuring R - T plots. Measurements of electroresistive effect in this state using low dc of different values and performed in cooling run reveal discontinuities of R - T plots. It is proposed formation of two different high resistive states: at low temperatures and at vicinity of T m . The discontinuities disclose switching between these two states initiated by substrate-induced long-range strain and by manifestation of memory effect. This interpretation of experimental results explains appearing of low temperature peak based on influence of the long-range strains on formation of high resistive interlayers in the film during the thermocycling. We argue that the interlayers acquire memory properties after being modified by martensitic-type transformations. DOI: http://dx.doi.org/10.5755/j01.ms.18.1.1333

Ti-4Fe-7Al 合金の焼戻しに伴う特異現象

Unprecedented phenomena were discovered by tempering the Ti-4Fe-7Al alloy quenched from the β (bcc) field. The alloy became very hard when it was tempered at 450℃ for several minutes, and severely rugged surface was generated. The inverse shape recovery phenomenon was also discovered when a quenched specimen that had been bent at room temperature was heated. The tempered microstructure showed almost β grains and some of the usual martensitic acicular structure areas. However, electron back scattering pattern (EBSP) measurements showed that the β-like grain was not the bcc structure but was the hcp or orthorhombic structure. X-ray diffraction (XRD) measurements clarified that an orthorhombic α″ structure (a=0.2995 nm, b=0.4913 nm, c=0.4659 nm) was formed from the β phase by tempering. Moreover, this α″ structure was confirmed to be a type of martensitic transformation because no concentration distribution was detected in scanning transmission electron microscopy-energy dispersive spectroscopy (STEM-EDS) analysis of the microstructure. It was suggested that the essential Ms point of the alloy should be higher than room temperature; however, the martensite transformation could not operate by fast quenching. The newly-discovered α″ martensite is formed without atomic diffusion by heating. When the β grain transforms into the single α″-variant, a very huge lattice strain is generated, resulting in the severely rugged surface or the inverse shape recovery phenomenon.

Phase Transformations in Ti-V-Cr-H Composition

Occurrence of phase transitions in TixVyCrz-H systems was analyzed versus temperature. Hydrogen evacuates from the hydrogenated compounds via two main steps. The 1st step corresponds to the destabilization of the fcc hydrogenated lattice leading to a fcc → bcc martensitic type transformation. The 2nd step occurs according to the decomposition of the resulting hydride via evacuation of hydrogen from the bcc lattice. Both the kinetics and temperature of 1st and 2nd step transformations depend on the composition of the starting TixVyCrz alloys.

Magnetoresistance and electroresistance of highly resistive states in thin nonhomogeneous La0.67Ca0.33MnO3 films

The magnetoresistive and electroresistive properties of thin nonhomogeneous La0.67Ca0.33MnO3 films have been investigated after thermocycling from 200 to 80 K. Highly resistive states with an additional low temperature resistance peak near 95 K were revealed in the films using probe currents as low as 1 μA. The film resistance at the peak is sensitive to the probe current strength and the applied magnetic field. The highly resistive state is metastable and is associated with the formation of martensitic inclusions during the thermocycling. The exhibition of memory effects during the cooling also suggests the idea of the presence of martensitic-type transformations.

Evidence of α → ω phase transition in titanium after high pressure torsion

Abstract It is well known that a high pressure ω-phase is formed in Ti at high pressures in the range between 2 and 8 GPa. This martensitic-type transformation demonstrates very large hysteresis, and hence the ω-phase can be retained in the material after release of pressure. Additionally, applied shear stresses are known to facilitate the α → ω transformation. This paper describes an investigation on the ω-phase formation after high pressure torsion under a wide range of pressures and shear strains by means of X-ray diffraction and transmission electron microscopy. We show that the ω-phase forms in Ti upon high pressure torsion deformation after 300 s under a pressure of 3 GPa. This suggests that the transformation kinetics are notably increased as compared with the kinetics of pressure-induced transformation.

Concerted Molecular Displacements in a Thermally-Induced Solid-State Transformation in Crystals of DL-Norleucine

Martensitic transformations are of considerable technological importance, a particularly promising application being the possibility of using martensitic materials, possibly proteins, as tiny machines. For organic crystals, however, a molecular level understanding of such transformations is lacking. We have studied a martensitic-type transformation in crystals of the amino acid DL-norleucine using molecular dynamics simulation. The crystal structures of DL-norleucine comprise stacks of bilayers (formed as a result of strong hydrogen bonding) that translate relative to each other on transformation. The simulations reveal that the transformation occurs by concerted molecular displacements involving entire bilayers rather than on a molecule-by-molecule basis. These observations can be rationalized on the basis that at sufficiently high excess temperatures, the free energy barriers to concerted molecular displacements can be overcome by the available thermal energy. Furthermore, in displacive transformations, the molecular displacements can occur by the propagation of a displacement wave (akin to a kink in a carpet), which requires the molecules to overcome only a local barrier. Concerted molecular displacements are therefore considered to be a significant feature of all displacive transformations. This finding is expected to be of value toward developing strategies for controlling or modulating martensitic-type transformations.

Defect generation of anatase nanocondensates via coalescence and transformation from dense fluorite-type TiO2

The anatase nanocondensates produced by energetic pulse laser ablation on Ti target under oxygen background gas have been observed by transmission electron microscopy. They were found to coalesce in approximately parallel orientation on the (001) plane to form dislocations and in twin orientation on the (112) plane to form faulty and twinned crystals. The anatase phase (denoted as a) was also derived from the dense fluorite-type (denoted as f) condensates by a martensitic-type transformation to form twin variants following the crystallographic relationship ⟨001⟩f‖[100]a with a habit plane close to {100}f‖(001)a for a beneficial lower interfacial strain energy. The f-a transformation route of TiO2 can be rationalized by a metastable phase change in terms of the intersection of the internal energy versus cell volume curves of the polymorphs.

Dynamic Behavior of Two Types of Martensitic Transformations in Cu-Al-Ni Shape Memory Alloy Single Crystal by Acoustic Emission Method

Dynamic behavior of two types of martensitic transformations during tensile deformation of Cu-Al-Ni shape memory alloy single crystal has been investigated using an acoustic emission waveform analysis. Two kinds of martensitic transformations consist of β1 ⇔ β1′ (structural change of DO3 to 18R) and β1 ⇒ γ1′ (structural change of DO3 to 2H), each of which is called super-elastic and thermo-elastic martensitic transformations, respectively. These two types of martensitic transformations could be obtained during tensile deformation because of different heat treatment. The rise time at the source (the source rise time) in finite elastic solid by the modified Takashima’s method was analyzed using the acoustic emission waveform detected during the martensitic transformation. The mean source rise time to the γ1′ phase was smaller than that to the β1′ phase before yielding and became the same after yielding. The former result means that the nucleation of the γ1′ phase is faster than that of the β1′ phase because of different crystallographic structure. The latter result is that the growth rate of the γ1′ phase is the same as that of the β1′ phase.

Stress-induced phase transformation and detwinning in NiTi polycrystalline shape memory alloy tubes

Deformation behavior associated with initial austenite (A), rhombohedral (R) and martensite (M) phase structures was studied in polycrystalline NiTi shape memory alloy tubes by tensile testing at different temperatures. The nominal stress–strain curves of the tubes from room temperature (23 °C) to 70 °C were recorded. The deformation of NiTi tubes with initial structure of R-phase proceeded via R → M martensitic transformation, while the deformation of NiTi tubes with initial structure of M-phase proceeded via martensitic detwinning. It was found that the R → M martensitic type transformation was realized, at the macroscopic level, by nucleation and growth of an inclined cylindrical band, while the detwinning process of the tube was macroscopically homogeneous. Further, two-stage yielding, which is associated with austenite to rhombohedral (A → R) and R → M phase transformations, was observed in the stress–strain curves of NiTi tubes in a certain testing temperature range. With a further increase in temperature, the shape of the nucleated band remained cylindrical until 60 °C (> A f) when the shape of the initial band suddenly became helical which was well observed in the superelastic microtubing.

An Approach to Developing a Force Field for Molecular Simulation of Martensitic Phase Transitions between Phases with Subtle Differences in Energy and Structure

d,l-Norleucine is one of only a few molecules whose crystals exhibit a martensitic or displacive-type phase transformation where the emerging phase shows a topotaxial relationship with the parent phase. The molecular mechanism for such phase transformations, particularly in molecular crystals, is not well understood. Crystalline phases that exhibit displacive phase transitions tend to be very similar in structure and energy. Consequently, the development of a force field for such phases is challenging as the phase behavior is determined by subtle differences in their lattice energies and entropies. We report an approach for developing a force field for such phases with an application to d,l-norleucine. The proposed procedure includes calculation of the phase diagram of the crystalline phases as a function of temperature to identify the best force field. d,l-Norleucine also presents an additional problem since in the solid state it exists as a zwitterion that is unstable in vacuo and therefore cannot be characterized using high-level ab initio calculations in the gas phase. However, a stable zwitterion could be obtained using Onsager's reaction-field continuum model for a solvent (SCRF) using both Hartree-Fock and density functional theory. A number of force fields and the various sets of partial charges obtained from the SCRF calculations were screened for their ability to reproduce the crystal structures of the two known phases, alpha and beta, of d,l-norleucine. Selected parameter sets were then employed in free energy minimizations to identify the best set on the basis of a correct prediction of the alpha-beta phase transition. The Williams' nonbonded parameters combined with partial charges from SCRF-Polarized Continuum Model calculation were found to reproduce the structures of the phases accurately and also maintained their stability in extended molecular dynamics simulations in the Parrinello-Rahman constant stress ensemble. Moreover, we were also able to successfully simulate the phase transformation of the beta- to the alpha-phase. The identified force field should enable detailed studies of the phase transformations exhibited by crystals of d,l-norleucine and hence enhance our understanding of martensitic-type transformations in molecular crystals.

On the study of the solid–solid phase transformation of TlBiTe2

The narrow gap semiconductor TlBiTe2 undergoes a solid–solid phase transformation from the rhombohedral (D3d) to the cubic (Oh) phase. The present paper deals with the study of this phase transformation combining the results of Differential Scanning Calorimetry (DSC) and Transmission Electron Microscopy (TEM). It has been found that during heating the transformation is an athermal activated process, which can be described only by a combination of more than one processes while during cooling it exhibits an expectable thermal hysteresis due to the volume difference. The results of the kinetic analysis combined with the electron microscopy findings, supported also by the Fourier Transform Infrared (FTIR) spectroscopy ones, lead to the conclusion that TlBiTe2 undergoes a multiple-step, displacive, martensitic type transformation.

The effect of nickel on the martensitic-type transformations of Pt3Al and TiPt

The effect of nickel on two classes of martensitic-type transformations in platinum systems has been studied. The first transformation is Ll 2 to DO c ' in the Pt3Al system and the second is B2 to B 19 in the TiPt system. The microstructures after transformation in the two systems are very different. The product of the Pt 3 Al transformation has a twinned microstructure, typical of cubic-to-tetragonal transformations. The product of the TiPt transformation is lath-like, although the morphology can be altered using heat treatments. The parent phase in the TiPt system is not retained at room temperature, whereas the parent phase in the Pt 3 Al transformation can be stabilised to room temperature. A great variation in hardness and transformation temperature is seen in each system as the composition is varied about the stoichiometric ratio, which has the lowest hardness. The Pt 3 Al transformation temperature has been reported to range from around room temperature to 1000°C. The TiPt transformation temperature can range from 1000 to 1080°C. The effect of nickel additions on these alloys also has a marked effect on the parent and product phase stability, and hence the microstructure and resulting hardness. The effect on the Pt 3 Al phase is complex, as nickel appears to stabilise the parent phase. The hardness varied in the region of 350 to 500 HV 10 . For the TiPt phase, the hardness values were generally found to increase with the nickel additions increasing from 250 to about 600 HV 10 . The addition of 20 at.% nickel decreases the transformation temperature from around 1000°C to about 600°C.